1. Field of the Invention
The present invention relates to photosensitive semiconductor nanocrystals, a photosensitive composition comprising semiconductor nanocrystals and a method for forming a semiconductor nanocrystal pattern using the same. More particularly, the present invention relates to semiconductor nanocrystals that are surface-coordinated with a compound containing a photosensitive functional group, a photosensitive composition comprising semiconductor nanocrystals, and a method for forming a semiconductor nanocrystal pattern by forming a film using the photosensitive semiconductor nanocrystals or the photosensitive composition, exposing the film to light and developing the exposed film.
2. Description of the Related Art
Due to the quantum confinement effects of compound semiconductor nanocrystals (i.e. quantum dots), the characteristic energy bandgap of semiconductor materials are changed. Since the control over the materials, structure, shape and size of the nanocrystals enables the control of the corresponding bandgaps, various energy levels can be obtained.
In recent years, there have been many trials to prepare semiconductor nanocrystals by a wet chemistry method wherein a precursor material is added to an organic solvent and nanocrystals are grown so as to have an intended size. According to the wet chemistry method, as the nanocrystals are grown, the organic solvent is naturally coordinated to the surface of the nanocrystals and acts as a dispersant. Accordingly, the organic solvent allows the nanocrystals to grow in the nanometer-scale level. Using vapor deposition processes, e.g., MOCVD (metal organic chemical deposition) and MBE (molecular beam epitaxy), it is difficult to uniformly control the size, shape and density of nanocrystals. In contrast, the wet chemistry method has an advantage in that nanocrystals can be uniformly synthesized in various sizes by appropriately controlling the concentration of precursors used, the kind of organic solvents, synthesizing temperature and time, etc.
However, since nanocrystals prepared by the wet chemistry method are commonly dispersed in an organic solvent, such as toluene or chloroform, techniques of forming a thin film as well as pattern forming method of nanocrystals are required in order to apply the nanocrystals to electronic devices. Patterning techniques reported hitherto are mainly associated with the patterning of nanocrystals by vapor deposition. These techniques, however, have a shortcoming in that control over the uniformity of size, shape, and density is difficult (Appl. Phys. Letter, 1997, 70, 3140).
In this regard, U.S. Pat. No. 5,559,057 suggests a method for forming a pattern of nanocrystals which comprises the steps of vapor-depositing or spraying nanocrystals using a mask to deposit nanocrystals only on the areas not covered with a mask, irradiating the nanocrystals with an electron beam to produce a thin film, and removing the mask. U.S. Pat. No. 6,139,626 discloses a method for indirectly forming a pattern of nanocrystals by filling in pores of a template with nanocrystals wherein the template may be patterned in any configuration. However, these patterning methods involve the use of a high-energy electron beam and a troublesome lift-off operation of the mask used. In addition, the template material may affect the performances of the pattern to be formed, and there is thus a limitation in the kind of materials that can be patterned.
Further, U.S. Pat. No. 5,751,018 discloses a method for aligning nanocrystals using terminal groups of a self-assembled monolayer formed on a metal substrate. U.S. Pat. No. 6,602,671 describes a method for binding dispersed nanocrystals to a polymeric support. Since the above-mentioned methods are not substantially associated with patterning, they have limited applicability to the patterning of nanocrystals.
Thus, there exists a need in the art for a method for forming a pattern of semiconductor nanocrystals in a simple manner, without the use of a template or a deposition process requiring high vacuum and high temperature conditions.